Method of purifying air

Abstract

A pre-purification method of feed air for cryogenic air separation, which includes; (a) an adsorption step wherein a compressed feed air is supplied in an adsorption column, wherein a moisture adsorbent and a carbon dioxide adsorbent are filled in this order from the side where the feed air is introduced in the column, to remove water and carbon dioxide from the feed air; (b) a decompression step wherein pressure in the adsorption column is reduced; (c) a heating step wherein the adsorbents in the decompressed column are heated and regenerated, and the heating step includes a total heating step wherein the moisture adsorbent and the carbon dioxide adsorbent are heated and a partial heating step wherein the moisture adsorbent is heated; (d) a cooling step wherein the adsorbents are cooled by introducing a purge gas, which is not heated, to the adsorption column; and (e) a pressurization step wherein the cooled adsorbents are pressurized by purified air.

The invention claimed is: 
     
       1. A pre-purification method of feed air for cryogenic air separation; wherein
 feed air is purified in succession with plural adsorption columns, and an adsorption step and a regenerating step are performed for the columns alternatively by switching the steps so that at least one of the columns is constantly treated in the adsorption step, the method including the following steps (a) to (e): 
 (a) an adsorption step wherein a compressed feed air is supplied in an adsorption column, wherein a moisture adsorbent which adsorbs water included in feed air and a carbon dioxide adsorbent which adsorbs carbon dioxide included in feed air are filled in layers in this order from the side where the feed air is introduced in the column, to remove at least water and carbon dioxide from the feed air; 
 (b) a decompression step wherein pressure in the adsorption column is reduced to atmospheric pressure after the adsorption step is terminated; 
 (c) a heating step wherein the moisture adsorbent and the carbon dioxide adsorbent in the adsorption column, which has decompressed to the atmospheric pressure, are heated and regenerated; 
 (d) a cooling step wherein the moisture adsorbent and the carbon dioxide adsorbent are cooled at a temperature, wherein an adsorption operation is performable, by introducing a purge gas which does not comprise water and carbon dioxide and is not heated; and 
 (e) a pressurization step wherein the cooled moisture adsorbent and the cooled carbon dioxide adsorbent are pressurized by purified air; wherein 
 the heating step (c) includes a total heating step and a partial heating step, which are performed in parallel, wherein 
 the total heating step is a step wherein a heated purge gas, which does not comprise water and carbon dioxide, is supplied to the discharged side of a purified air of the adsorption column to heat the moisture adsorbent and the carbon dioxide adsorbent, and 
 the partial heating step is a step wherein heated raw air is supplied between a layer of the moisture adsorbent and a layer of the carbon dioxide adsorbent to heat the moisture adsorbent; 
 and wherein a temperature of the purge gas which is supplied to perform the total heating step in the step (c) is 100 to 250° C. 
 
     
     
       2. The pre-purification method of feed air according to  claim 1 , wherein a temperature of the raw air which is supplied to perform the partial heating step in the step (c) is 60 to 250° C. 
     
     
       3. The pre-purification method of feed air according to  claim 1 , wherein the amount of raw air supplied to the partial heating step in the step (c) is 5 to 15% with respect to the amount of air which is treated in the pre-purification. 
     
     
       4. A cryogenic air separation method which includes the pre-purification method of feed air according to  claim 1 .